Hot rolling of steel wire rod requires high rolling speeds in order to obtain the large tonnages required today at economical production rates. In addition to the demand for high speed, users demand larger and larger coil weights in order to save handling costs in the later handling of the wire rod for wire drawing, cold heading, etc.
Steel wire rod of medium to high carbon content requires heat treatment before it can be drawn into wire. It has become more and more common to perform this heat-treating in line with the rolling, utilizing the heat in the rod as it exits from the last finishing stand for heat-treating purposes. Several such in-line patenting processes are known, most of them utilize forced air-cooling of the wire after forming the wire into loops, which later are collected into coils. In order to make the air-cooling effective, the loops must be spread out sidewise on a conveyor belt, or kept as round separated loops. The best known of these in-line patenting processes is so-called "Stelmor" process which is described, for instance, in U.S. Pat. No. 3,231,432. In this process, the coil is spread on a moving conveyor, and later after cooling collected into coils. This process allows for the high rolling speeds, and also makes large coil sizes possible, which only are limited by the size of the collecting mechanism, as well as by the billet size. This process suffers from the disadvantage or difficulty of obtaining absolutely even cooling of all parts of the coils, for instance, the parts of the coils which overlap on the moving conveyor are not subject to the same cooling as the remainder of the coil. Air cooling also causes problems because of varying ambient air temperature and humidity. Finally, the spread-out of the coils causes difficulties in forming good coils for future handling because of the spring effect of the spread-out coils forcing the coils into wrong shapes. This is especially pronounced in coils having a high carbon level, say from 0.50% and up.
Another process for in-line patenting of hot rolled wire rod is described in U.S. Pat. No. 3,669,762. In this process, termed the "ED" process, the hot coiled rod is put directly into a water tank where a vapor barrier forms around the wire rod and delays cooling in a critical transition period of the metal. This process is a batch process with two coilers per rolling stand with the rod from alternate billets being switched to alternate coilers. This switching causes serious problems at high rolling speeds, such as 10,000 f.p.m. or more, which is becoming common today.
This type of in-line patenting could also be modified so that the coils will spread out on a moving conveyor belt under water. Thereby, it would be possible to attain the ability to roll unlimited coil weights at high speeds. However, problems of forming good coils of high carbon steels would remain.
A further problem when rolling wire rod at high speeds is to change the direction of the rod emerging from the mill so that it is properly received by the coiler. The reason for this difficulty is that especially low carbon rod is very soft and will start buckling and cause trouble in the mill whenever an effort to change its direction is made.
It is preferable to direct the rod vertically downwardly into the coiler, whereas the rolling mill commonly produces the wire rod emerging in a horizontal plane. This necessitates a change in the direction of the rod. In order to achieve this change in direction of the wire rod without causing cobbles, the most successful method up to now has been to feed the wire into a conveyorlike structure having a curved shape with the conveyor running at exactly the same speed as the wire rod. This method, however, causes great difficulties in synchronizing the conveyor with the wire rod, and the conveyor also suffers from very rapid wear at high wire rod speeds.